Stop in for a cup of coffee

toolmanmike said
I know mine has the ribs. No vent though.

I think that's generally the deal on the better ones; ribs or vent, and sometimes brass - which maybe last a little longer under hard use.

I noticed the Motorcraft caps for my AMC engine are ribbed but not vented.

My guess is they decided the venting lets the ionized air out and there's no reason for te more expensive casting???